This disclosure is generally directed to toner processes, and more specifically, emulsion aggregation and coalescence processes, as well as toner compositions formed by such processes, and development processes using such toners.
In a number of electrophotographic engines and processes, toner images are applied to substrates. The toners may then be fused to the substrate by heating the toner with a contact fuser or a non-contact fuser, wherein the transferred heat melts the toner mixture onto the substrate. However, the quality of the developed image may vary depending upon, amongst others, the toner composition properties, the age of the toner (measured in how many print cycles have been completed using the toner composition), and how the toner composition reacts to changes in the operating conditions, such as temperature and relative humidity.
Many current toner formulations show charging that is temperature and humidity specific. For example, many toner formulations perform moderately in ambient (70° F., 20% RH) and low temperature, low humidity (60° F., 10% RH) conditions, but their performance worsens in high temperature, high humidity (80° F., 80% RH) conditions. Satisfactory performance over a broader range of conditions is desired, because the toner composition can be subjected to a range of different operating conditions, while high print quality is still demanded.
Proposed solutions to this problem have been to incorporate a charge control agent (CCA) in the toner composition, either by adding a charge control agent as an external additive to the toner particle surface, where the charge control agent is blended on top of the toner particles, or adding the charge control agent directly into the toner particles as an internal additive. However, incorporation into the toner did not enhance the charge sufficiently, and addition as an external additive did not result in consistent charging properties over time as the toner composition ages. Neither approach has provided an effective solution of providing consistent toner particle charging over time.
This problem is in turn aggravated by the increasing demands placed on the toner development process. For example, electrophotographic engines and processes are being implemented that demand higher print counts, where the toner composition has an increased lifetime in terms of the number of imaging cycles. However, for many toner compositions, the demand of higher print counts has resulted in the problem that additive impaction into the surface of the toner particles increases, detracting from the objective of longer print life. As toner ages past 10,000, 20,000, and even 30,000 prints, the additives become impacted in the toner surface to the extent that charges are reduced and print failure increases.
Thus, a need exists for toner compositions that provide more consistent charging properties over the lifetime of the toner. A need also exists for toner compositions in which the additives do not become so impacted into the toner particle surface before the end of life of the cartridge, thereby allowing for better print performance and consistency in a broader range of temperature/humidity zones and for improved cartridge life.